This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Objective: To study population differences in vocal communication and vocal development in wild pygmy marmosets (Cebuella pygmaea). There has been little evidence of vocal plasticity in nonhuman primate calls. However, investigators of vocal communication in wild primates have rarely studied more than one population and thus potential differences in vocalization may not be evident. We are studying five populations of pygmy marmosets in the upper Amazon basin in Eastern Ecuador. We have found significant differences in the structure of long calls and trills in each population, after correcting for individual differences. This is the first evidence of variability in vocal structure in non-provisioned monkeys (ruling out human intervention as a source of change). We have also made detailed measurements of environmental noise and how sounds are degraded in each of the habitats and have found that some of the differences in call structure can be related to habitat differences. We have also found population variation in the species of trees used for exudate feeding and can refute several ecological hypotheses for this variation. This suggests that social learning may account for population differences in exudate feeding preferences. In addition, we are studying the "babbling" of young infant marmosets to learn more about vocal development, and we are studying predator alarm calls. This research used WNPRC Library and Information Services. Funding ended before this reporting period;a publication has resulted.